The present invention relates to an electromagnetically actuated flow control valve.
Flow control valves of numerous variety are available that provide many types of flow characteristics, often tailored to specific applications. These valves typically provide a single flow performance slope characteristic over the valve's full range of flow rates. A single slope valve does not suit the requirements of a flow system where very precise control is desired over a low flow rate range and controlled, low restriction flow is desired over a high flow range.
In order to achieve high flow rates a valve must have a relatively large flow path. A large flow path diminishes a valve's ability to provide precise control under low flow rate conditions. Therefore, to provide both high flow and precisely controlled low flow characteristics, two parallel valves are typically used in a flow system when these functions are required. Valves have been designed with a plurality of flow paths each including an obturator that act as two separate parallel valves to provide dual flow slope characteristics.
An example of a flow system that requires both high flow and precisely controlled low flow characteristics is a vehicle's evaporative emission control system. Valves used as purge valves in vehicle evaporative emission control systems are generally solenoid or vacuum-diaphragm actuated and include those operated by a pulse-width modulated signal to provide variable control of purge flow rates.
Purge valves operate to selectively open a normally closed communicative passage between the evaporative emission control system's storage canister and the induced vacuum of an internal combustion engine's intake system. The working fluid is an air and fuel vapor mixture in varying ratios. Due to the varying proportionality of the air and fuel vapor in the fluid mixture and the range of engine operating states, precision flow control capabilities are required of the purge valve.
A vehicle's engine operates at various states and under a wide range of conditions. The fuel supply system is closely controlled and under some specific, identifiable, operating conditions the introduction of collateral fuel vapors from the evaporative emission control system is undesirable. One such vehicle operating condition where an evaporative emission control system canister purge must be executed with precise flow rate control to assure desirable engine performance is engine idle.
It is preferable to provide a means of precisely controlling purge flow at low flow rates during non-preferred purge states including engine idle to minimize unwanted effects, while providing controlled high flow rates at engine operating conditions more amenable to purge flow. Therefore, a valve that provides these flow control characteristics is needed.